1. Field of the Invention
The present invention relates generally to an inflator or gas generator for an air bag or other safety device and, more specifically, to a compact multi-level output inflator or gas generator which can selectively release gas at different rates and levels and thus enable the air bag or another type of safety device to be deployed or operated at different output levels in accordance with different sensor inputs.
2. Description of the Related Art
Recently, there has been a demand for controlling the rate and amount of inflation or operation of safety devices such as air bag restraint systems in accordance with variables such as passenger size, position, seat belt usage and the velocity of a vehicle at the time of collision.
In order to provide optimal occupant protection, different levels of output are required from the airbag inflator. For example, in a high-speed collision with a large unbelted person, full rapid inflation of the air bag is required to provide the best restraint. In lower speed crashes with smaller sized occupants or even out-of-position occupants, a lower, slower rate of inflation is required so as not to inadvertently injure the occupant but still provide enough inflation to effect appropriate restraint.
In currently available air bag inflators intended for multi-level or variable output function, the performance is accomplished primarily with inflators which are made up of two individual inflators of the same type that may share one manifold, or by individual propellant chambers in a common pressure vessel sharing one common manifold.
Utilizing two separate inflators of the hybrid type, for example, results in large, heavy and expensive designs since nearly every component is duplicated. For example, there are two distinct pressure vessels, with redundant closures, seals, and in some cases diffusers or manifolds. Additionally, there is the added requirement of securing the two inflators to a common platform, which in turn increases cost, weight, and complexity in manufacturing.
The second approach of having separate propellant chambers encapsulated in one common pressure vessel results in more efficient packaging and reduced cost if the components are shared by the two propellant charges. To achieve different levels of inflation, it has been proposed in U.S. Pat. No. 3,773,353 to Trowbridge et al. to provide two separate charges and to ignite one in the event that a slow inflation is required and to ignite both in the event of a high speed collision, thus achieving the very rapid inflation and deployment of the air bag which is necessary under such circumstances. In this device the charges are arranged within a housing which is filled with a non-toxic gas under pressure. This housing is sealed by a burst plate that is punched out by a piston and rod type of arrangement when a first of the two charges is detonated. This arrangement suffers from the drawback of being relatively complex and therefore, relatively expensive. For example, no less than three burst plate arrangements are necessary. Also, the charges are each isolated from the reservoir and reservoir gas by an inner housing and a respective rupturable closure.
U.S. Pat. No. 3,905,515 to Allemann discloses another multi-stage inflator assembly which utilizes two separate charges and which disposes the charges in a chamber which is used to store a non-noxious gas under pressure. However, this arrangement is even more complex than that in U.S. Pat. No. 3,773,353. In this arrangement a portion of the burst disc forms the head of a slidable shuttle valve member which is projectable into an exhaust passage to partially throttle the outflow of gases following a detonation of one or both of the two charges.
Consequently, there is a need for a cost-effective, lightweight, compact, simple multi-level output inflator or gas generator for air bags and the like. This need is met by the new and improved multi-level output hybrid inflator and gas generator of the present invention.